Rubber compositions having reduced permeability to air and other gases have utility in many applications, including pneumatic tire inner liners, tire inner tubes and curing bladders, and various other types of air bladders. A halobutyl elastomer, either alone or in combination with other synthetic and/or natural rubbers, is the most often utilized rubber, which together with a carbon black are the major components of low permeability rubber compositions.
With respect to inner liner compositions, it is known that carbon black not only reduces the air permeability of such compositions, but also affects other important inner liner performance characteristics such as, for example, adhesion of the inner liner to the reinforcing plies comprising the tire carcass, the heat resistance, flex resistance and compression set of the inner liner. There is, however, a maximum loading of the grades of carbon black conventionally used in formulating inner liner compositions, which if exceeded will adversely affect the inner liner. For example, two grades of furnace carbon blacks commonly used in formulating inner liner compositions, ASTM N660 and ASTM N772, are incorporated in amounts which generally do not exceed 60 parts by weight of black per 100 parts by weight of rubber.
U.S. Pat. No. 3,639,308 discloses an inner liner composition which exhibits satisfactory air permeability and which includes as much as 120 parts by weight of carbon black per 100 parts by weight of rubber. A disadvantage is that the composition incorporates thermal grade carbon blacks which are made by the not widely used thermal process.
PCT Patent Application No. WO 94/05732 discloses rubber compositions containing carbon blacks of the type disclosed in the present application. However, there is no disclosure of the use of these rubber compositions for reducing gas permeability.